Detergent compositions in tablet form are known in the art. It is understood that tabletted detergent compositions hold several advantages over granular detergent compositions. Examples of such advantages include ease of handling, transportation and storage. Tablets are therefore required to be of sufficient hardness such that they do not crumble or disintegrate on handling, transportation or storage.
Detergent tablets are traditionally prepared by the compression or compaction of granular detergent compositions. It has however, been found that solubility of the tablet generally decreases with increasing compression/compaction force. Detergent manufacturers have directed tablet development efforts toward striking a balance between strength and solubility.
The most common method used by detergent manufacturers for increasing tablet hardness is to increase the compaction pressure of the machinery employed to tablet the detergent composition. This process, although providing tablets of sufficient hardness, results in tablets that suffer from a reduction in rate of dissolution in water. Henkel EP-0170791 describes a process for making a tablet detergent composition comprising per compounds and tabletting aids. The detergent composition is compacted at a pressure of 5.times.10.sup.7 to 10.sup.8 Pa resulting in tablets having a breaking strength of between 50 and 120 N.
Other methods of controlling tablet hardness and dissolution have been discussed in the prior art. Detergent manufacturers have for example, introduced alterations in the detergent formulation, thereby changing the characteristics of the tablet. Henkel WO93/00419 describes increasing tablet hardness by providing a detergent composition comprising polymer. Unilever EP-0466484 and EP-0522766 describe increasing tablet hardness by providing a tabletted detergent composition comprising liquid binder and particles of specific size ranges. Japanese patent application Kao J06207199 A describes a process for making a detergent composition in tablet form wherein the process consists of the mixing nonionic surfactant and an oil absorbing material, granulating the mixture to provide particles of specific size and density, then compacting the resulting particles to form a tablet. Henkel EP-0579659, describes a process for preparing a detergent tablet wherein the alkaline detergent additives are agglomerated with builder, water and nonionic surfactant resulting in a tablet having a high break strength.
It is thus the object of the present invention to provide a detergent composition in tablet form that is sufficiently hard to meet handling, transportation and storage needs, without negatively affecting the rate of dissolution of the tablet.
The present invention provides a process for making a detergent composition in tablet form, wherein the tablet produced has increased hardness. Detergent tablets comprise a particulate base detergent matrix and liquid components.
It has surprisingly been found that by selectively applying the low viscosity non-aqueous liquid components of a detergent composition onto a specifically selected high porosity fraction of the particulate base detergent matrix harder tablets are produced. It is believed that the non-aqueous liquid components of a tablet detergent composition act as lubricants at the surface of the components of the particulate base detergent matrix. These components, once provided with additional lubrication, slide over each other more easily reducing the potential for particulate fusion during the tabletting step. It is therefore, the aim of the present invention to reduce such lubrication and increase tablet hardness. It is believed that the non-aqueous liquid components are held within pores of the particulate base detergent matrix, increasing tablet hardness by providing liquid bridges which effectively bind particulate components together.